<template>
	<ul class="list">
		<li
		 class="item"
		 v-for="item of letters" 
		 :key="item"
		 :ref="item"
		 @touchstart="handleTouchStart"
		 @touchmove="handleTouchMove"
		 @touchend="handleTouchEnd"
		 @click="handleLetterClick"
		 >
		 {{item}}
		</li>
	</ul>
</template>

<script>
export default {
	name: 'CityAlphabet',
	props: {
		cities: Object
	},
	computed: {
		letters() {
			const letters = []
			for(let i in this.cities){
				letters.push(i)
			}
			return letters
		}
	},
	data () {
		return {
			touchStatus: false,
			startY: 0,
			timer: null
		}
	},
	updated () {
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleLetterClick (e) {
			this.$emit('change',e.target.innerText)
		},
		handleTouchStart () {
			this.touchStatus =true
		},
		handleTouchMove (e) {
			if(this.touchStatus){
				if(this.timer){
					clearTimeout(this.timer)
				}
				this.timer = setTimeout (() => {
					const startY =this.$refs['A'][0].offsetTop
					const touchY = e.touches[0].clientY - 79
					const index =Math.floor((touchY -startY)/20)
					if(index>=0 && index<this.letters.length)
					this.$emit('change',this.letters[index])
				},16)
			}
		},
		handleTouchEnd () {
			this.touchStatus =false
		}
	}
	
}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.styl'
	.list
		display: flex
		flex-direction: column
		justify-content: center
		position: absolute
		top: 1.58rem
		right: 0
		bottom: 0
		width: .4rem
		.item
			line-height: .4rem
			text-align: center
			color: $bgColor
</style>
